So I could walk into a Law office and if I talk a good game I'll get hired without having passed the bar? If not, then it is a part of the hiring process, as it is a pre-interview filter.
Most large firms draw their entry-level associates from their pool of summer interns, which they hire two years before they graduate law school and take the bar exam. They also usually give people a mulligan on failing the bar exam the first time, so people might work somewhere for 6+ months before passing the bar.